This invention relates to semiconductor devices, for example, optical semiconductor devices such as photodetectors.
Semiconductor devices, such as photodetectors, often include a wire bond for providing electrical connection to the active regions of the device. Since pressure and ultrasonic energy are applied to effect the bond, the wire bonding process can lead to damage to the device resulting in such undesired characteristics as increased leakage current. In order to avoid this problem, it has been proposed to provide the wire bond pad at some portion away from the active area.
To be effective, such bond sites are desirably formed in a manner which keeps additional capacitance to a minimum. This is of particular significance for high speed devices. It is known that capacitance is a function of the area of the pad, the dielectric constant of the insulating layer over which the pad is formed, and the thickness of the insulating layer. Therefore, one of the design criteria is to use an insulating layer with as low a dielectric constant as possible (known in the art as low k dielectric material) which can be applied with an adequate thickness. Desirably, the dielectric constant is no greater than 3 and the thickness is at least 4 xcexcm.
Use of low k dielectric materials, however, presents additional problems in the fabrication of the devices. In particular, metals generally adhere poorly to the low k dielectrics and conventional wire bonding techniques utilizing ultrasonic energy leads to low yielding manufacturing processes. Although metal deposition can be effected by sputtering to alleviate the metal adhesion problem, the simple and convenient method of a lift-off process to define metal patterns is not compatible with common sputtering processes. Further, if conventional sputtering is employed to deposit metal, often a conductive interface is produced on the whole surface of the low k dielectric (through a chemical reaction of energetic metal particles) and hence making it virtually impossible to devise a suitable manufacturing process to define a confined metal bond pad.
Furthermore, usually bond pads are thick (2-4 xcexcm) and hence makes sputtering an unattractive method of manufacturing as compared to conventional electron beam evaporation which is known in the art as having much higher deposition rates.
Unfortunately, if high rate sputtering is employed, substrate temperature may use rise high enough to cause surface degradation of low k dielectrics and eventually lead to potential long term reliability problems.
It is desirable, therefore, to provide a method and optical device utilizing low k dielectric materials.
The invention in accordance with one aspect is a semiconductor device including a semiconductor substrate, an active region in the substrate, a first low dielectric constant insulating layer formed over at least a portion of the substrate, a second insulating layer formed over at least a portion of the first insulating layer, and a bond pad formed over the second insulating layer and electrically contacting the active region.
The invention in accordance with another aspect is a method of fabricating a semiconductor device including the steps of forming an active region in a semiconductor substrate, forming a first low dielectric constant insulating layer over at least a portion of the substrate, forming a second insulating layer over at least a portion of the first layer by deposition at a temperature no greater then 200xc2x0 C., and forming a bond pad over the second insulating layer.